Critical review of normative framework for seismic assessment of existing masonry buildings

Abstract

The multiple elements that receive and transfer the lateral loads and their interconnectivity form the lateral load path of a structure. When a structure is subjected to seismic loads, every element in the load path is tested. Load path determines the order of component capacities and the hierarchy of failure in a structure. Hence, identification of load path forms the fundamental step in the assessment of any structure. However, for unreinforced masonry (URM) buildings, the lack of a well defined and continuous load path makes it difficult to set an assessment protocol. The fundamental load paths and the role of participating elements are not always properly understood and therefore, structural assessment of existing unreinforced masonry (URM) buildings has been an area of challenge. Further, the variation in construction typology and non-uniformity in material properties across the world created difficulties in bringing uniformity to these assessment guidelines. Although the global scheme of assessment is similar to other structural types, the thin line of separation that exists between the onset of different mechanisms and the multiple interactions that happen between these mechanisms and associated elements alter the load paths in an existing structure. However, from time to time, observations made during earthquakes have necessitated revisiting the load paths and mechanisms in URM structures and modifying the assessment guidelines. The fundamentals of seismic assessment procedures across the world show similarities with each other but the differences observed are also substantial. Hence, a critical review of the normative assessment procedures is carried out to understand the similarities and limitations in code-based assessment procedures and to identify the scope for refinement in existing methodologies.